1. Field of the Invention
This invention relates to an error removal system to be used for a data backup tape recorder.
2. Prior Art Background
A conventional tape recorder for data backup applications normally stores and retrieves data in and from as many as 9, 15 or 18 tracks on a single magnetic tape by means of a magnetic head, which comprises as integral parts thereof a writing section realized by winding a wire around a core having a writing gap and a reading section realized by winding a wire around a core having a reading gap which is wider than the writing gap. The writing section and the reading section are arranged in a direction parallel to the running direction of the magnetic tape and are operational for a single channel. For writing data on a magnetic tape by such a data backup tape recorder, the writing section of the magnetic head writes a reference signal on the central track that provides a reference and then data on this and other tracks by following a certain procedure.
For retrieving the data from the magnetic tape, on the other hand, the reading section of the magnetic head reads the reference signal and then seeks a target track on the magnetic tape specified by the reference signal so that the magnetic head starts reading the data from that track. When an error is found in the data being retrieved, the tape recorder immediately stops the magnetic tape, winds it back and moves the magnetic head upward or downward by a certain distance before it restarts the data retrieving operation by means of the related reading section of the magnetic head.
Recently, there have been proposed data backup tape recorders that can store data and retrieve data in and from as much as 26 tracks on a single magnetic tape. As schematically illustrated in FIG. 7, magnetic head 11 of such a tape recorder comprises, as integral parts thereof, a pair of erasing sections each having a core around which a wire is wound, a pair of writing sections each having a core around which a wire is wound, the cores of the writing sections being respectively provided with writing gaps 13a, 13b, and a pair of reading sections each having a core around which a wire is wound. The cores of the reading sections are respectively provided with reading gaps 14a, 14b. The writing section having the writing gap 13a and the reading section having the reading gap 14a are arranged along the running direction of the magnetic tape in this order and constitute respectively a writing section and a reading section for a lower channel, while the writing section having writing gap 13b and a reading section having reading gap 14b are arranged along the direction opposite to the running direction of the magnetic tape in this order and constitute respectively a writing section and a reading section of an upper channel. The writing sections and the reading sections for these two channels are arranged at a predetermined pitch in a direction perpendicular to the running direction of the magnetic tape. The width of the cores of the writing sections is 178 .mu.m and that of the cores of the reading sections is 127 .mu.m, which is considerably smaller than the width of any conventional cores which is normally 267 .mu.m.
For a data backup tape recorder of this known type, a magnetic tape 19 provided with a number of marks comprising a BOT (Begin Of Tape) mark 15, an EOT (End of Tape) mark 16, an EW (Early Warning) mark 17 and a LP (Load Point) mark 18 as illustrated in FIG. 6 is used. Each of the marks 15 through 18 is, in fact, one (or more than one) hole(s) formed through the tape 19 and arranged along the center line of the upper half portion and/or that of the lower half portion of the tape as seen in its running direction. The BOT mark 15 and the EOT mark 16 are respectively located at the front and rear ends of magnetic tape 19, whereas the EW mark 17 and the LP mark 18 are located on the center line of the upper half portion of magnetic tape 19 and separated respectively from the BOT mark 15 and the EOT mark 16 by a given distance toward the middle of the tape. For storing data in a magnetic tape 19 by a data backup tape recorder of this type, magnetic tape 19 is moved rightward and the writing section of magnetic head 11 as seen in Figure having writing gap 13a for writing data in the lower channel is activated so that a reference signal having a specific frequency f.sub.o is written in reference signal recording area 20 immediately after BOT 15 located on the center line of the lower half portion of the magnetic tape 19 and then data are written in data recording area t0 located after said reference signal recording area 20.
Thereafter, magnetic tape 19 is moved leftward and the writing section of magnetic head 11 having writing gap 13b for writing data in the upper channel is activated so that a reference signal with frequency f.sub.o is written in reference signal recording area 21 immediately after EOT 16 located on the center line of the upper half portion of the magnetic tape 19. Then data are written in data recording area t1 located after said reference signal recording area 21. Then, again, magnetic tape 19 is moved rightward and the writing section of magnetic head 11 having writing gap 13a for writing data in the lower channel is activated so that a reference signal having a specific frequency f.sub.1 is written in reference signal recording area 22 immediately after BOT 15 located on the center line of the lower half portion of the magnetic tape 19. Then data are written in data recording area t2 located after the reference signal recording area 22. Thereafter, magnetic tape 19 is moved leftward and the writing section of magnetic head 11 having writing gap 13b for writing data in the upper channel is activated so that a reference signal with frequency f.sub.1 is written in reference signal recording area 23 immediately after EOT 16 located on the center line of the lower half portion of magnetic tape 19. Then data are written in data recording area t3 located after the reference signal recording area 23. In a similar manner, magnetic tape 19 is moved alternately rightward and leftward so that reference signals with frequency f.sub.1 and data are recorded by means of the magnetic head 11 respectively in reference signal recording areas 24, 25, . . . 31 and data recording areas t4, t5, . . . t11 in the upper and lower half portions of magnetic tape 19. Then magnetic tape 19 is again moved alternately rightward and leftward so that data are written by means of magnetic head 11 in data recording areas t12, t13, . . . t24 in the upper and lower half portions of magnetic tape 19. Finally, magnetic tape 19 is moved rightward so that reference signals with frequency f.sub.1 and data are respectively recorded in reference signal recording area 32 and data recording area t25.
For retrieving the data stored in magnetic tape 19, magnetic head 11 of the data backup tape recorder is moved in a direction perpendicular to the running direction of the tape to seek the track of the tape that stores the data to be retrieved and the data stored in the data recording area of that track is then read out by means of the reading section having reading gap 14a or 14b, whichever appropriate, of magnetic head 11. More specifically, if the track that stores the data to be retrieved is in the lower half portion of magnetic tape 19, the tape will be moved rightward and the reading section having reading gap 14a will be used for data retrieval, whereas the tape will be moved leftward and the reading section having reading gap 14b will be activated for retrieving data stored in any of the tracks in the upper half portion of magnetic tape 19.